Have recently done up my 21 with the usual upgrades of pipes, reed valves, rear head conversion etc. Yesterdays race weekend went well, but there are some issues with excess fuel/unburnt fuel.

When I came in after each session there was fuel almost dripping out of the cans. Initially I thought main jets, but with the helpful interpretation of a two stroke mechanic parked next to me I did a plug chop which showed a nice burn on the plugs. So it seems that there is not an issue with overfueling at high revs. And it definitely runs well, will rev the whole way up and lift a wheel with no issues, and faster than my brothers set up Aprilia (go Honda!).

However it does bog down heavilly between 7-8.5k and the abovementioned mechanic suggested that the main jets were probably good, but the pilot jets may be too large. Is this a likely cause of the excess fuel/unburnt fuel symptoms, or is it likely to be something else?

I'm not after specific jetting advice, just some helpful information. If it is indeed a specific question of jetting I will ask in the members forum.

Cheers guys!

Fuel coming out of the pipes is most often caused by sitting for a while when the float valves haven't shut off the fuel, so the carbs overflow into the crankcase and that excess fuel is pushed through the engine.

Not sure how that could happen after a race though!

Maybe you better start by telling us the exact modifications...

Not too sure about the excess fueling. Especially after coming in off the track with a nice coloured plug chop?? Maybe check the float levels?

That 7-8.5k rev range is where the power valves and air correction solenoids really kick in.
I would be tempted to check these out to make sure they are working properly?

Sorry, I can't be of much help on this one.
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Dave Ett wrote:Fuel coming out of the pipes is most often caused by sitting for a while when the float valves haven't shut off the fuel, so the carbs overflow into the crankcase and that excess fuel is pushed through the engine.

Not sure how that could happen after a race though!

Maybe you better start by telling us the exact modifications...

Yeah I thought of that, and it seems possible that perhaps it could fill between races? That would have to be quite a flow of fuel within an hour though. Is there a simple way to check if the valves are sealing?

Re. Float levels, forgive my ignorance but how would the level cause the symptom? Would it push more fuel though the jets?

Specific mods are: Tyga exhaust, Tyga reed valves, rear head conversion, standard oil pump and standard power valve adjustment (which is working I believe - well it was when I checked yesterday morning). Jetting I obvious can't really discuss but the power jets have been blanked and mains adjusted.

So the suggestion of too large pilot jets isn't valid you fellas don't think?

Oh and the bogging down may not be related, I just thought I'd mention it if it could be related to the fuel dripping out of the cans.

Do you mean the exhausts are actually full of fuel or do you just have wet pipe ends which drip a few spots of black 2T jizz?

My bike has always had wet pipe ends after a run and if you hold your hand in front of the exhaust whilst the engine ticks over you get wee black spits all over it after a while. Yet it still pulls to the redline etc etc. No wheelies though...

You wouldn't happen to be bringing it to Manfeild on Saturday would you?

Satchriossi wrote:Do you mean the exhausts are actually full of fuel or do you just have wet pipe ends which drip a few spots of black 2T jizz?

My bike has always had wet pipe ends after a run and if you hold your hand in front of the exhaust whilst the engine ticks over you get wee black spits all over it after a while. Yet it still pulls to the redline etc etc. No wheelies though...

You wouldn't happen to be bringing it to Manfeild on Saturday would you?

I couldn't say if they were 'full' of fuel, but there is enough coming out the back that I need to wipe it up (I am pedantic though as you know). Plus it weeps out around a couple of the rivets in the end cans close to where they bolt on to the chambers. I have to wipe it up too. But yeah, it's not like its pouring out or anything. Sounds similar or slightly worse than what yours does.

But it didnt do that (that I can remember) before I put the new parts on. Or at least I'm pretty sure it didn't. And I exaggerate, it won't pull anything like a big wheelie, just a little lift in 1st and maybe 2nd.

Not going to Manfeild im afraid, have to work the saturday in Auckland and the drive would be a killer to get back sunday night...

When I said 'Maybe check the float levels?',.. it was a "clutching at straws" thing as indicated by the question marks.
My thinking was that if the float levels were set too high, and you had it jetted to give a good plug chop, then possibly?? this may result in it running a bit rich at mid range throttle settings?? But I am just making wild guesses here.
I can't really see why an "upgrade of pipes, reed valves, rear head conversion etc." would cause excess two-stroke spooge.
Maybe you changed to a 2T oil that doesn't burn as well?
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Without getting into a jetting conversation, it sounds miles too rich to me, probably done your mods and gone tooooo safe.
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TuckerBag wrote:When I said 'Maybe check the float levels?',.. it was a "clutching at straws" thing as indicated by the question marks.
My thinking was that if the float levels were set too high, and you had it jetted to give a good plug chop, then possibly?? this may result in it running a bit rich at mid range throttle settings?? But I am just making wild guesses here.
I can't really see why an "upgrade of pipes, reed valves, rear head conversion etc." would cause excess two-stroke spooge.
Maybe you changed to a 2T oil that doesn't burn as well?

Yeah I get what you mean there, and that's what it seemed to me. I'll pull the carbs apart and check the floats when I get some time. Two stroke oil is the same as before. Castrol TTS.

Any of you guys, do you get the same thing? Oil/fuel in the end of the cans (enough to have to wipe out every session)? Maybe I'm worrying about it too much.

As for too rich, I'm sure it is conservative so you might be right. Seems odd to get a positive plug chop result though if it's too rich though right?

I need another test day!